1. Field of the Invention
The present invention relates to an apparatus for measuring fluid loss characteristics and, more particularly, to an apparatus for dynamically testing fluid loss characteristics of test fluids such as drilling fluids.
2. Description of the Prior Art
The drilling fluid, commonly referred to as drilling mud, used in the drilling of oil and gas wells, serves a number of purposes such as lubricating the bit, removing the cuttings from the borehole, etc. To accomplish its purposes, the drilling mud should, ideally, possess certain characteristics. For one, it should be capable, if desired, of depositing a coating on the wall of the borehole, the coating being commonly referred to as a filter cake. The filter cake serves to stabilize the borehole and prevent loss of the liquid portion of the drilling mud through the walls of the borehole into the adjoining formations. This loss of liquid from the drilling mud commonly referred to as fluid loss is a function of many variables such as the composition of the drilling mud, the types of formations encountered in the drilling process, temperatures and pressures in the borehole, etc.
It has long been the desire to be able to test drilling muds under simulated borehole conditions in an attempt to determine characteristics such as fluid loss. For example, British Pat. No. 1,363,793 discloses an apparatus for determining dynamic fluid loss trends in drilling fluids while U.S. Pat. No. 4,538,452 discloses an apparatus for measuring filter cake qualities of a drilling fluid under dynamic conditions.
Neither of the two cited patents, nor any of the other prior art known to Applicant, discloses an apparatus for dynamically testing the fluid loss characteristics of a drilling fluid or the like which can simulate borehole conditions such as high temperature and high pressure together with a simulation of the shearing action experienced by the drilling fluid during the actual drilling operation.